There is significant perinatal morbidity and mortality associated with polyhydramnios and oligohydramnios because currently available therapies have limited efficacy. Yet, effective reduction of amniotic fluid (AF) volume and prevention of preterm delivery in pregnancies with polyhydramnios reduces neonatal morbidity and mortality. Similarly, increasing AF volume in laboring patients with reduced AF improves fetal outcome. The proposed studies will ask a number of questions about strategies to alter AF volume which potentially may be applied clinically for treatment of poly- or oligohydramnios. Our previous studies provided valuable insight into physiologic mechanisms of maternal-fetal-AF water and electrolyte exchange. Whereas AF is maintained by a balance of sites of fluid production and resorption, fetal urine flow is the single most important site influencing AF volume. Thus, alterations in urine flow and perhaps other fluid exchange sites may be utilized to modulate AF volume. We have developed two novel, ovine experimental models to alter AF volume, each utilizing the selective arginine vasopressin (AVP) antidiuretic agonist [desamino, D-Arg8]-AVP (dDAVP). Preliminary ovine and human studies have supported the potential clinical utility of these interventions. Firstly, we hypothesize that intraamniotic dDAVP administration will result in increased fetal plasma dDAVP levels, reduced fetal urine and lung fluid production and decreased AF volume. Intraamniotic dDAVP represents a promising treatment for patients with polyhydramnios. Secondly, as the antithesis of dehydration we hypothesize that maternal intravenous dDAVP will induce maternal and fetal plasma hypo-osmolality, marked increases in fetal urine flow rates, and expansion of AF volume. Thus maternal dDAVP represents a potential therapy for patients with oligohydramnios. We will explore acute and chronic effects of intraamniotic (fetal) dDAVP and maternal dDAVP-induced hypo-osmolality. Physiologic assessments will focus on measurements of fetal fluid exchange (urine flow, lung liquid, swallowing, placenta diffusion permeabilities) and fetal plasma and AF volume and composition in normal pregnancies and models of poly- and oligohydramnios. We also will measure the effects of elevated dDAVP on fetal and maternal renal AVP receptor populations and on other fluid regulatory hormones (atrial natriuretic factor, renin- angiotensin). The goal of this project is to identify safe and effective treatments which can reliably alter AF volume in cases of poly- or oligohydramnios.